Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS

Improved understanding of controls of variability of tropical Pacific carbon and radiocarbon

Partners UPMC and LSCE of the NOCES project used an ocean general circulation model was used to test if sea surface C-14 behaves as a thermocline proxy in the eastern equatorial Pacific. For this study, these NOCES partners included C-14 as a passive tracer in the OPA-ORCA2 circulation model, which they forced with reanalysis fluxes during 1948 to 1999. Model results were compared to a previously reported coral record of Delta C-14 collected in the Galapagos Islands. The model reproduces the abrupt increase in the seasonally minima of Delta C-14 that was obsered in 1976-1977. In contrast to previous proposals that have attempted to explain this shift, these NOCES results indicate that increase is associated with neither a shift of thermocline depth over the NINO3 region, nor a change in the relative proportion of Northern vs. Southern source waters. Rather, it is due to a decrease in the Sub-Antarctic Mode Water (SAMW) component of the up-welling water via a decrease in entrainment of water from below the base of the directly ventilated thermocline.

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